Acidizing deep high-temperature wells



cRoss REFERENCE SEARCH Room July 22, 1969 D. H. FLICKINGER ACIDIZING DEEP HIGH-TEMPERATURE WELLS Filed Oct. 11. 1967 DON H. FLICKENGER INVENTOR.

BY au? /M ATTORNEY United States Patent O U.S. Cl. 166-302 7 Claims ABSTRACT F THE DISCLOSURE A deep high-temperature well is acidized in` a process including the steps of: (1) breaking down the formation by pressure applied only through the tubing; (2) opening a port in the tubing wall near the formation to be treated; (3) circulating cool fluid down outside the tubing and up inside the tubing, or vice versa, to temporarily cool the metal equipment in the well and the surrounding fot'- mations; (4) injecting acid down the tubing to acidize the formation; and, preferably, (5) isolating the tubing from the annulus by closing the port in the tubing wall following the treatment.

As wells are drilled deeper, acidizing of potential producing formations penetrated by the wells has become more difficult. One of the principal problems is the high temperatures in deep wells. High temperatures cause more rapid corrosion of metal equipment in the wells by acids used for acidizing. Inhibitors are available which are rather highly effective at temperatures up to about 200 F. However, even the best inhibitors now available begin to lose their effectiveness at temperatures very much above 200 F. Many wells are now completed in formations having temperatures well above 300 F.

The problem is particularly severe when acidizing with higher concentration acids. This problem is discussed in an article, High-Concentration Hydrochloric Acid Aids Stimulation Results in Carbonate Formations. This article is by Harris et a1. and is published in the Ioumal of Petroleum Technology for October 1966, starting on p. 1291. On p. 1295 ofthe article, it is suggested that enough pre-flush be used to cool the formations so that acid is injected at temperatures suiciently law so that available corrosion inhibitors are effective. Itfis undesirable to inject water into formations producing oil or gas. Injecting the waters'in the aqueous acid solution is undesirable, but necessary. It is even more undesirable to inject a large enough 'volume of water as a pre-flush to cool the metal equipment in the well and the formation surrounding the well. This is particularly true, of course, if concentrated acid is to' be used. Water used as a preflush can also dilute the concentrated acid in the formation and thus largely negate the beneficial effects that would otherwise occur from using concentrated acid.

An object of this invention is to provide a method for decreasing the corrosion which takes place when acidizing a deep high-temperature well. A more specific object is to provide a method for cooling a deep high-temperature well before acidizng, thus avoiding use of a pre-flush. Still other objects will be apparent from the following description and claims.

In the drawing, a cross sectional view of the well equipment required for performing my process is shown.

3,456,733 Patented July 22, 1969 ICC In general, l accomplish the objects of my invention by opening a port through the tubing wall at a level near the formation to be'acidized and circulating a cooling liquid down inside the tubing and up outside the tubing or vice versa. This cools not only the metal parts of the well, but also the formations surrounding the well. This circulation can be continued for as long a period as desired. Th-us, as much cooling as required can be provided without displacing the cooling fluid into the formation.

Considering the drawing in more detail, casing l0 is sealed in the well by cement 11. Tubing string 11 extends into the casing and packer 13 is set between the tubing and casing strings. Above the level of the` packer, a port 14 is provided in thewall of the tubing string. This port can be closed by sleeve valve 15. Suitable equipment is shown and described in more detail in U.S. Patent 2,716,454 Abendroth, and in my U.S. Patent 3,244,234.

Using this apparatus in my process, the tubing valve is initially in the closed position. A liquid is then intro-` duced through the tubing to the formation to be treated. Since the casing is isolated from the tubing, high surface pressures normally required to break down the formation can be safely imposed. Pressure is applied to break down the formation. The valve is then opened and a cooling fluid is pumped down the tubing and up the annular space between the tubing and casing. As soon as the well has been cooled to the desired temperature, acid is introduced down the tubing and forced into the formation to be treated.

Many variations and alternates are available in my process. For example, the formation may be broken down initially with an aqueous acid solution, water, oil,

, emulsions, or other well known fracturing compositions.

The cooling -uid may be gaseous, such as air or natural gas, but preferably is a liquid, such as water or crude oil. The circulating rate of the cooling liquid and the length of time it is circulated may vary between wide limits depending upon circumstances. Examples of the amount of cooling obtainable by circulating are to be found in the article A Practical Evaluation of Cements for Oil Wells," by R. lloyd Farris, starting on p. 283 of Drilling and Production Practice (1941), published by the American Petroleum Institute. The liquid may be chilled to a temperature below surface atmospheric temperature before circulating it in the well, if desired. In critical cases, a wireline bottom-hole recording thermometer can be run into the well to be sure the temperature has been lowered to the desired extent. d The aqueous acid solution maybe ordinary hydrochloric acid solutionof from about 5 to about 35 percentv by weight strength. It may also be other acids, such as acetic acid, chloracetic acid, or uophosphoric acid, as described in U.S. Patent 2,742,092 Bond. All the acid may be introduceddown the tubing or down the annular space between the tubing and casing or through both si-` multaneously. Concentrated acid may, for example, be pumped down the tubing while water is pumped down the annular space between the tubing and casing. By controlling the flow ratesin the tubing and annulus, any desired acid concentration can be produced when the two streams mix at the bottom of the well. However, an advantage of this technique is that the subsurface temperat-ure can be reduced a sufficient amount so that concentrated acid may safely be injected down both the tubing and annulus simultaneously.

Any of the better acid corrosion inhibitors, such as those described in U.S. Patents '3,107,221 Harrison et al., 3,077,454 Monroe et al., or the like, may be used to decrease the rate of corrosion of metal equipment in the well by the acid.

Handling of the well after acid is injected depends upon whether the well is an oil well, a gas well, a water well, an injection well in a waterooding process, a waste disposal well, or others which will occur to those skilled in the art. Any of the various well completion processes used after acidizing any such wells may be used depending upon the circumstances. An advantageous step following acidizing is simply to close the port to isolate the tubing from the annulus, thus placing the well in condition to produce oil, gas, or the like.

The description above has been concerned with use of the tubing string and the annular space between the tubing` and casing as the two conduits, or flow passages, through which cooling fluid is circulated. It will be apparent, however, that the passage between the tubing and casing can be replaced by a second string of tubing, if desired. The important features are a tubing packer connected to a string of tubing to provide one liow passage extending from the top of the well through the packer, and a second flow passage connected to the interior of the tubing above the packer through a port which can be opened or closed.

The main advantages of my process are usually the reduction of the rate of corrosion of metal parts by acid used in acidizing and making feasible the use of concentrated acid which has been shown to effectively decrease the rate of reaction of the acid with the formation so that the acid penetrates theI formation farther before it is spent. The process has other purposes and advantages, however, such as attaining high injection rates by using both the tubing and annulus as injection conduits for the stimulating lluid being pumped.

Many other variations, alternates and advantages will occur to those skilled in the art. Therefore, I do not wish to be limited to those described above, which are given bylwty of example only, but only by the following claims.

c aim:

1. In the method of acidizing a deep high-temperature well in which a string of tubing extends into the well and provides a passage extending through a packer set in the well above the formation to be treated, and in 'which a second passage is provided into said well, said second passage being connected into said first passage above said packer but near said formation by means of a port which can be opened and closed, the improvement comprising:

breaking down said formation with pressure applied only down said rst passage with said port closed, opening said port,

circulating a cooling dund down one of said passages and up the other to cool the well equipment and formations surrounding said well, and, while the well equipment is cool,

injecting acid down at least one of said passages and into said formation.

2. The method of claim 1 in which said second passage is the annular space between the tubing and casing in the well.

3. The method of claim 2 in which, in the step of injecting acid down the well, concentrated acid is injected down the well inside said tubing and water is simultaneously injected down the annular space between the tubing and casing and through said port and is mixed with said concentrated acid to form a more dilute acid before said acid enters said formation.

4. The method of claim 2 in which, in the step of ini y 5. The method of claim y1 in which injection of acid isy l followed by closing said port to isolate the inside of the tubing from the annular space vbetween the tubing and casing.

6. In the method for acidizing a deep high-temperature Iwell in which a packer is set in the well close to and above the formation to be treated, the packer being set on a string of tubing extending from the earths surface and connected to said packer, and in which a port is provided in the tubing above but near said packer, said port being capable of being opened and closed, the improvement comprising:

breaking down said formation with pressure applied only through said tubing string with said port closed, opening said port, circulating a cooling liquid down the well inside the tubing and up the well inthe annular space between the tubing and casing to cool the well equipment an formations surrounding the well, and

while the well equipment is cool, injecting concentrated acid down the well inside the tubing and simultaneously down the annular space between the tubing and casing.

7. The method of claim 6 in which injection of acid is followed by closing said port to isolate the inside of the tubing from the annular space between the tubing and casing.

References Cited UNITED STATES PATENTS 2,143,251 l/1939 Savitz 166-42 2,259,428 10/ 1941 Shelley 166-39 2,716,454 8/ 1955 Abendroth 166--42.1 2,772,737 12/1956 Bond et al. 166-39 X 3,301,326 l/1967 McNamer 166-39 X 3,354,957 1l/1967 Every et al 166-39 OTHER REFERENCES Kingston, Benson M., Acidizing Handbook, Houston, Tex., Gulf Pub Co. (1947), p. 48.

Harris, O. E., et al., High-Concentration Hydrochloric Acid Aids Stimulation Results in Carbonate Formations, in J. Petroleum Technology, October 1966, pp. 1291- 1296.

CHARLES E. OCONNELL, Primary Examiner I. A. CALVERT, Assistant IExaminer U.S. Cl. X.R. l66--307, 308 

